Algae Suppression Mechanism

Frank Lawler

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Apr 15, 2009
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:This is from an earlier discussion on the Aquaria Central forum
I have never understood how a tank with healthy plants in nutrient laden water can have far less algae than a tank with zero nutrients in the water column. This is at the same time both true yet counterintuitive. Then I came across an article on plant allelopathy.
This concerns the process by which plants release chemicals that either benefit or inhibit the growth of their neighbors. Perhaps our healthy plants are somehow producing and releasing their own natural form of algecide.

Mr Barr responds:
If you add active carbon or do large water change= no allelopathic chemicals, thus there's the control. See any evidence that using activeated carbon or doign large water changes somehow...induces algae blooms?

My reply:
I'm still stuck on trying to understand why a planted tank with nutrient-rich water has far less algae than one without either. A shaky hypothesis: IF there is such a thing as a natural algacide secreted by plants, and IF it lurks in exactly the same place as living or dormant algae, then might water changes or carbon filtration reduce both concentrations equally, thereby leaving the balance bewtween the two essentially unchanged, although at lower concentrations?
Like so many on this forum, I would never think of questioning Mr. Barr. I am simply very curious as to the exact mechanism by which healthy plant growth defeats algae

Question
Would anyone care to comment? I am a new member and this is my first post. Thanks.
 

dutchy

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Welcome:

you could read this: http://www.barrreport.com/showthrea...any-significant-effect-on-algae-in-aquariums? As well make a search on allelopathy
Also: http://www.tropica.com/article_fullscreen.asp?type=aquaristic&id=531

I always understood it's "what is the signal to make the algae germinate" which is a situation that makes it have a chance to complete it's life-cycle. Nutrients will not make the algae germinate. When one lacks, it does. So it's not about what's in the water, but what's missing.

No NO3=BGA
No PO4=GSA
No CO2=BBA

So basically as long as we concentrate on plant growth, which is providing all the nutrients, we have no algae. So it would be an indirect effect.

Now I'm not one of the guru's here, (which can correct me if I'm wrong) but "it's my 2 cents"

Regards,
dutchy
 
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Biollante

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Busted Link

Hi Frank, Dutchy,

Unfortunately the link to Ole's Refute is busted, it is the best explanation I have ever seen.

Biollante
 

shoggoth43

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Dutchy's reply sounds about right based on my limited understanding. I also wouldn't worry too much about questioning Tom about things. He wouldn't be here if he didn't want people to ask questions. Just be polite. :) Anyone who does science for a living, as opposed to "science" or SCIENCE, expects to be asked questions which might turn things on their head. If not, then they'd never question their findings and just keep going in the wrong direction. It keeps everyone honest and often leads to a "duh" moment here and there but gets us all just that bit further. Just read around a bit first and then ask your questions.

Alleopathy is one of those odd things. It "SHOULD" work that way and does work that way with things like corals and some terrestrial plants but it's harder in the aquatics since it's much easier to show a nutrient imbalance or shading or other cause first and then you have to prove the chemical warfare that "ought" to be going on is having some effect, but I don't think anyone has really proven this yet. The assumption is that it's there, and with certain plant combinations might, or might not be relevent. In any event, the practical result is that carbon or lots of Water Changes makes the alleopathy question less of a concern. Welcome aboard. Ask around. :)

-
S

dutchy;50272 said:
Welcome:

you could read this: http://www.barrreport.com/showthrea...any-significant-effect-on-algae-in-aquariums? As well make a search on allelopathy

I always understood it's "what is the signal to make the algae germinate" which is a situation that makes it have a chance to complete it's life-cycle. Nutrients will not make the algae germinate. When one lacks, it does. So it's not about what's in the water, but what's missing.

No NO3=BGA
No PO4=GSA
No CO2=BBA

So basically as long as we concentrate on plant growth, which is providing all the nutrients, we have no algae. So it would be an indirect effect.

Now I'm not one of the guru's here, (which can correct me if I'm wrong) but "it's my 2 cents"

Regards,
dutchy
 

Tom Barr

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You can also see that carbon is central to plant cutin production and stability, so sloughing off of the epicuticular waxes on some species might be the key, other species, simply grow faster than the algae can colonize.
So you trim off the old bottom sections and replant the tops. Most of these have less cuticle than the slower growing species.

Why don't you have nasty fungal and bacteria injections on your skin?
It sloughs off continuously. The same could be the case for aquatic plants.

The algae that bug us are epiphytes, so they must recruit to a surface.
Wood, non living materials are not an issue.
Various herbivores, bleach etc can address that.

There are at least 2-3 different things that could be the reason.
Allelopathy is way down on this list. There's just too few chemicals and not in high enough concentrations given the wide massive range of plant species.
How could all 300-400 species produce roughly the same effects in many aquariums with many combos of species?

Secondary chemicals like allelopathic products are pretty specific. Now why would these chemicals target just algae and not other plant species?
Again, we see no such evidence of plant- plant interactions, if fact, we see the opposite in mixed communities of plants.

In fact, epiphytes are less susceptible to such compounds:
http://www.sciencedirect.com/scienc...serid=10&md5=d065cd47b96fbc1f959a8b943ae5b662

Light is the main compeitive factor with the species we mess with. Phytoplankton are rarely an issue.
Also, these are only a few species that show this effect, we do not know the specific species of algae, and also have little in the way of CO2 stability in these systems, or light.
clearly light being 10-200X less, and CO2 being 10X more will have some rather large effects on algae, and on plant growth.

As the article mentions, in situ measures are radically different from crushed extracts in test wells, that;'s where Diana Walstad focused some of her suspicions. I find them hard to verify in light of activated carbon and water changes.
Those would be the experimental controls since they would remove those allelopathic chemicals as dependent factors.

There are many more alternatives than the chemical solution to possible causes.

Regards,
Tom Barr

Regards,
Tom Barr

Regards,
Tom Barr